odor from direct vent Buderus boiler

This is my first post and I definitely need some help with this ODOR problem, please...

I just had a new Buderus direct vent boiler with a separate hot water tank installed into my new room addition's basement. My old boiler was tankless and vented into the chimney of the main basement.
I was told there wouldn't be any odor detected in my home and would "possibly" smell a slight odor outside if in the vicinity of the vent. I can smell an exhaust like odor at times even when my windows are not fully open. The installer came back and reset some factory presets. The odor is still present at times.
Today, while sitting in the new room above the boiler, a terrible exhaust odor came directly into the room when the windows were open.
Is there anything that can be done to minimize the odor besides keeping the windows closed at all times? Any suggestions on what we can do now?
I have also smelled the same odor isolated in my second floor masterbath when the window was closed, but did not smell it in the adjacent bedroom. Is there any way the odor can come through the plumbing?

Which venting option did they use? I have one, and don't notice it, but then again, I rarely open windows.

The thing burns extremely clean. Did they run the dual pipe setup where it is closed combustion? Did they put a trap on the exhaust for the condensate? Did they fill the condensate trap with water first? (although it would fill itself after running for awhile - internally, it does hold a fair amount of water to ensure that the trap actually doesn't get blown dry by the exhaust fan, until that happens, it would leak exhaust gasses).